The SMOLT predated the M686. People wanted a S&W frame and action with a full lug barrel to control recoil.

The advent of the 686 did away with the need for a custom proposition.

S&W has not had a big problem copying other manufacturer's ideas when they appear to have been successful. Examples such as the 1911, the ASP conversion, the Python's barrel and the Taurus Judge are legion.

Then again, lots of people have copied S&W too.